Finally, Michael Phelps broke something that wasn't a world record — HIS ASS — taking a nasty spill while crowd surfing in a Vegas nightclub this week.

Phelps — who's STILL in party mode after the London Games — hit up XS nightclub Monday night, and for some reason thought it would be a good idea to crowd surf inside an inflatable raft.

Beautiful. For the record, Phelps is about 6-4, 200 pounds, so, even if he was being egged on, it was probably foolhardy to expect a crowd of drunken concert attendes to pass him and a friend around on a life raft. Tough to imagine what could have given Michael Phelps that kind of skewed perception.